Uncertainties of aging after the injection of microscale zero valent iron (mZVI) into subsurface hinder the widespread application of this technology into in-situ groundwater remediation. As TCE removal by mZVI is usually accompanied by mZVI anaerobic reaction with water, this study investigated the hydrogen evolution kinetics, TCE removal performance, and electron efficiency (EE) of mZVI particles under single and combined effects of organic geochemical constituents (humic acid (HA)), inorganic constituents (hardness (Ca 2+ ) and alkalinity (HCO 3 − )) in groundwater. The results showed that both H 2 generation and TCE removal were enhanced in the presence of HA (5–20 mg L −1 as DOC), and significant delay of aging precipitates formation was supported by SEM-EDS, XRD and XPS depth-profiling characterization. With increasing Ca 2+ -HCO 3 − concentrations (0.4–2 mM), the mZVI corrosion were inhibited for the formation of a thin compact passive film on mZVI surface. Furthermore, in co-presence of organic and inorganic constituents, the negatively-impacted iron corrosion kinetics suggested that promotional effects of organic constituents were dwarfed by the inhibitory effects of inorganic constituents. In addition, the EE values in different systems ranged among 1.31–7.40%, and decreased significantly with time. Hence, these findings provide insight into aging mechanism and performance prediction of mZVI under different groundwater geochemical conditions.
Kai Yu,Xiuqiong Yang,Mao Wan,Haowen Jiang,Penghui Shao,Liming Yang,Hui Shi,Xubiao Luo
This study, for the first time, evaluates a novel method for the desorption of contaminants from soil that uses the heat generated by zero-valent iron (ZVI) under low-frequency electromagnetic fields (EMF), and elucidates the specific effects of soil pH upon the process. It was found that the temperature of soil mixed with ZVI could reach up to ∼60 °C within 20 min under the applied EMF, and after 60 min the residual fraction of m-xylene in soil decreased by 86.4% compared to no-ZVI soil. The most efficient desorption of m-xylene occurred at a soil of pH 5. Desorption was related to the net heating capacity of the ZVI particles, which was defined by pH-dependent formation of surface corrosion products. The preservation of metal iron and formation of Fe(II) species was favored for heat generation. Soil pH also affected m-xylene retention and the local thermal conduction from ZVI to m-xylene by regulating the surface properties of fulvic acid and ZVI. This study provides valuable information regarding the impact of pH on the thermal desorption of soil contaminants by ZVI coupled with EMF and illustrates the potential of the method in the remediation of contaminated sites.
In this work, zero-valent iron particles supported on nitrogen doped porous carbon (Fe-NPC) was successfully prepared by a green and convenient one-pot method through pyrolysis. In Fe-NPC/PS system, 96.44% orange II (OGII) was almost removed within 35 min, which was much higher than NPC and Fe-PC of 53.27% and 54.67%, respectively. Factors influencing the degradation process of OGII were investigated, including PS concentration, catalyst dosage, initial pH and ions disturbance. The radical quenching studies, electron paramagnetic resonance (EPR) measurements and chronoamperometry experiments verified the degradation mechanism of OGII in Fe-NPC/PS system included both radical and non-radical pathways in which • HO and SO 4 -· were the dominant active radicals and electron transfer was involved. Fe-NPC exhibited excellent tolerance toward a wide pH conditions with only 88 µg/L iron leaching in initial pH of 3.1, which was much lower than literature reported. The low iron leaching of Fe-NPC was attributed to the protection of carbon matrix and doped nitrogen in catalyst. Moreover, the surface C O group of the catalyst contributed to better performance in alkaline system. Furthermore, the supported iron species introduced magnetism into the catalyst for easily separation. The Fe-NPC/PS system also exhibited high removal efficiencies for Congo red (CR), Reactive blue 19 (RB 19), 4-Nitrophenol (4-NP) and tetracycline (TC). These results provided a sight for economically and efficiently fabricating stable iron based nitrogen doped porous carbon catalyst for water contaminant degradation.
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